1. Field of the Invention
There is a present increasing interest and need in being able to assay or monitor a wide variety of organic compounds. Included among compounds of interest are drugs which are employed in the treatment of diseases or aberrant conditions, drugs of abuse, naturally occurring compounds involved with bodily functions, pollutants, trace contaminants and the like. The concentrations of interest of most of these compounds are generally of the order of 1 .mu.g/ml or less. In many instances, the environment in which these compounds are found include one or more compounds of similar structure, which must be distinguished from the compound of interest.
A body of techniques which have evolved are referred to as competitive protein binding assays. These assays rely on the ability of a receptor, usually an antibody, to recognize a specific spatial and charge conformation. The binding of the receptor to a ligand allows for a discrimination between bound and unbound ligand. By employing a labeled ligand and allowing for competition between labeled ligand and ligand in the unknown for the receptor, one obtains a distribution of the receptor between labeled and unlabeled ligand. By employing appropriate labels, one can distinguish between bound labeled ligand and unbound labeled ligand so as to relate this ratio to the amount of ligand in the unknown. When receptor is to be measured, substantially the same technique is employed, except that receptor is not added and one need not add unlabeled ligand.
In developing competitive protein binding assays a number of factors must be considered. Ease of preparation of the various reagents is an important consideration. The manipulative steps involved in the assay are also important, since it is desirable to minimize the opportunities for operator error. Stability of the reagents is also a significant consideration, as well as compatability of the system with presently available equipment. Of course, one is also interested in the accuracy and dependability with which the small concentrations of the materials are measured.
2. Description of the Prior Art
U.S. Pat. No. 3,817,837 teaches a homogeneous enzyme immunoassay. U.S. Pat. Nos. 3,654,090, 3,791,932, 3,850,752 and 3,839,153 teach heterogeneous enzyme immunoassays. In the agenda for the Ninth Annual Symposium on Advanced Analytical Concepts for the Clinical Laboratory, Mar. 17 and 18, 1977, Oakridge National Laboratory, a paper entitled "Phospholipase C-Labeled Antihuman IgG: inhibition of enzyme activity by human IgG," presented by R. Wei and S. Reib is reported. U.S. Pat. Nos. 3,935,074 and 3,998,943 disclose immunoassay techniques involving steric inhibition between two different receptors for different epitopic sites. Carrico et al, Anal. Biochem. 72, 271 (1976) and Schroder, et al, ibid 72, 283 (1976) teach competitive protein binding assays where a label is bonded to a hapten with the label being subject to enzymatic transformation to produce a signal. Antibody bound to the hapten inhibits the approach of enzyme to the label.